Official Blizzard Quote:

Prepare yourselves for battle as the bloody struggle between the Horde and the Alliance continues on Pandaria’s shores!

The first PvP season of World of Warcraft: Mists of Pandaria begins tomorrow, October 2! Once realms have come back up from scheduled maintenance, Matchmaking (MMR), Team, and Personal Ratings will be reset and players will able to compete in level-90 Arenas and Rated Battlegrounds for the best PvP gear, items, and titles.

I'm happy to hear Matchmaking (MMR) was reset. To be honest I was a little worried that they wouldn't do this.

Season 12 should begin for EU on October 3 similar to other maintenance in the past.

Just so you know, that was how they did it in Cata and if i remember correctly even wrath. The last time there was a weapon for the first season of a new expac was BC. I am probably wrong about wrath...